Final answer:
Valve replacement is the treatment of choice for a regurgitant bicuspid aortic valve when it is severe and causing symptoms or affecting the heart's function.
Step-by-step explanation:
A bicuspid aortic valve is a type of heart valve abnormality where the valve has only two cusps instead of the normal three. When the regurgitation is severe and causing symptoms or affecting the heart's function, valve replacement is recommended as the treatment of choice. This involves removing the defective valve and replacing it with an artificial valve. Valve replacement improves blood flow and helps prevent complications associated with regurgitation.